The long term objective of this proposal is to understand the molecular mechanism of pain syndromes resulting from peripheral nerve injury (neuropathic pain). These pain states represent major problems affecting the quality of daily life of patients with dental and orofacial disorders. These disorders do not typically respond to conventional analgesics. Unfortunately, the molecular mechanisms of neuropathic pain are poorly understood and, as a consequence, there are no specifically targeted, effective pharmacological agents available for neuropathic pain treatment. Our preliminary data indicate a correlation between increased mRNA levels in sensory neurons of neuronal nitric oxide synthase (nNOS), an enzyme that catalyzes the production of nitric oxide (NO), and the development of neuropathic pain (allodynia) in a rat model of peripheral nerve injury. This suggests that neuronal-derived NO may serve as a second messenger in the processing and/or modulation of neuropathic pain and regulation of nNOS expression at the level of transcription or mRNA processing may underline the neuronal plasticity following peripheral nerve injury. This research proposal is designed to further study the mechanism and functional role of nNOS expression to the development of neuropathic pain using tissues of dorsal root ganglia (DRG) and spinal cord from a rat neuropathic pain model. Molecular, immunohistochemical and pharmacological techniques will be utilized. The specific aims of this proposal are:. 1) To examine a possible genetic linkage between development of neuropathic pain and expression of nNOS by comparing the nNOS mRNA and protein levels in a rat strain that does not develop allodynia with those in a rat strain susceptible to allodynia development. 2) To examine the cellular mechanism of nNOS regulation and its relation to the development of neuropathic pain by examining contributions of axoplasmic transport, feedback inhibition and nerve discharge on the regulation of nNOS and neuropathic pain development. 3) To correlate expression of nNOS protein with its mRNA levels at intervals during the development of allodynia and to examine the cellular localization of nNOS in DRG and spinal cord of rats with neuropathic pain.